In the case of various surgical implants such as articulatedly connected, multipart bone plates and osteosynthetic vertebral column fixation devices where, for example, a longitudinal carrier extending approximately parallel to the vertebral column has to be attached by means of a number of bone screws, the joint-like connections must be releasably lockable. For this purpose, resilient tension members, such as collet chucks, are used. The locking of such joint-like connections is realized by means of an expansion of these resilient tension members within a corresponding cavity with fixed dimensions. This expansion process of resilient tension members is preferably achieved by means of clamping cones or clamping wedges.
An osteosynthetic fixation device including a bone screw to be anchored in a bone, a longitudinal carrier, and a connection member by means of which the bone screw is attachable to the longitudinal carrier. One example of such a device is shown in Patent No. WO 94/00066 to Schläpfer. This fixation device comprises a resilient clamping member shaped in the form of spherical segment contained between two parallel circles which has a conical bore, and a bone screw having a male taper corresponding to the conical bore of the clamping member and a screw thread arranged in the end portion located opposite to the bone. In the connecting member, a spherical cavity for receiving the clamping member is provided which is adequately dimensioned so as to permit the spherical segment of the clamping member to be pivotably received therein. A second bore serves for receiving the longitudinal carrier. The tightening of a nut screwed over the screw thread formed in said end portion of the bone screw and supported by the clamping member causes the taper formed in the bone screw to be pulled into the inner cone of the clamping member, thus spreading said clamping member apart and pressing it firmly against the wall of the spherical cavity, whereby the connecting member and the bone screw are kept in place relative to each other.
A disadvantage common to all these connections realized by means of clamping cones consists in the difficulties encountered in releasing said connections, which often necessitates heavy hammer blows to be struck on the bone screw or the connecting member or which requires the aid of special instruments.
The invention relates to a clamping connection based on a cone mechanism or wedge mechanism which is apt to be locked and released again by means of a screw driver.